Support is requested to continue fine structural investigation of: (1) the "cytomusculo-skeletal-adhesive system" in developing epithelial cells; focusing on filamentous and intramembranous structures which provide integrity within desmosomes and hemidesmosomes; and (2) intra-and intermembranous elements of triadic junctions of skeletal muscle. In desmosomes and hemidesmosomes, freeze-fracture will be utilized to study fine traversing filaments as vehicles for anchorage of tonofilaments to the cell membrane, and as related to two known populations of desmosomal and hemidesmosomal intramembranous particles. Similar means will be used to examine the interaction of membranes at these sites with extracellular adhesive materials. In triadic junction, the research will involve freeze-fracture analysis of intramembranous subunits recently demonstrated in our laboratory. These probably are important links in excitation-contraction coupling over this junction. An experimental approach is planned to test triadic junctional morphology under various states of muscular contraction. Projects secondary to main approaches include: (1) analysis of potential causal relations among the subcomponents of developing hemidesmosomes; and (2) continued exploration, using freeze-fracture techniques, of subcomponents of other junctions involving membrane-microfilament association.